The invention relates to a profiled casing for a roller press for subjecting particulate material to be ground 5 to high-pressure treatment, to a process for producing said profiled casing and to the use of a defined iron alloy having a high chromium content for producing said profiled casing.
For the comminution of particulate and brittle material to be ground, it is known to comminute the material to be ground not by shear stress—as is conventional but rather in an energetically economical manner solely by the application of high pressure in a roller nip. In addition to its energetically favorable use, this type of comminution also has the further advantage of an increased service life of the rollers used to generate the pressure in the roller nip.
In the comminution of rock and very hard and abrasive clinker, there is a predetermined limit to the service life of a roller of a roller press, however, which is caused by the severe abrasion brought about by the material to be comminuted. In the comminution in the roller nip, it is important in addition that the material to be ground passes through the roller nip uniformly and in a controlled manner. For relatively low abrasion and for improved and uniform entry of the material to be ground into the roller nip of the roller press, a process has therefore been adopted whereby the opposing rollers of the roller press are profiled. In the simplest case, this involves longitudinal grooves extending in the axial direction on the surface of the roller, in which compacted material to be ground accumulates to form an autogenous wear-resistant layer and which leads to a more uniform entry of material, even when the material to be ground has a broad grain size distribution or a grain size distribution which varies on average over time.
The structure of a roller for a roller press typically consists of a main roller body with shafts arranged thereon. No special demands are made of the main body in respect of material properties. A casing having the surface quality mentioned in the introduction is then shrunk onto said main body or fastened thereto with other means known to a person skilled in the art. This casing is a substantially cylindrical hollow body of a size on its inner side which is compatible with the main roller body, and on its outer side the casing bears a usually subsequently applied profiling.
DE 10 2004 043 562 A1 discloses an annular casing for a roller press which consists essentially of a nodular cast iron and which has a bainitic microstructure with residual austenite. This material is known for use for producing relatively small individual engine parts made of cast iron and is characterized on the one hand by ductility and on the other hand by a hard surface which forms during use. This material is generally referred to as ADI (Austempered Ductile Iron). On account of its properties, this material is outstandingly suitable for use in roller presses, but involves the disadvantage that the metallic microstructure must not be heated significantly above 400° C., so as not to prompt any undesirable phase transformation of the metallic microstructure. This phase transformation leads to significant changes in the physical properties of said material, and therefore the suitability of the material for use in a roller press deteriorates.
Since a casing is generally shrunk onto a main roller body, it is necessary to heat the casing. Under workshop conditions, it is possible to control slow and uniform heating without individual regions of the casing being overheated and therefore the local material properties thereof being changed in the process. This is different at the operating site of the roller presses. To heat the casings at the operating site, use is generally made of flame sources which heat the casing slowly and uniformly. In this heating process, the surface of the casing can be heated significantly above 400° C. when no provisions are made for preventing overheating. The controlled heating requires qualified and trained personnel, who are not always present at the operating site of the roller presses.
A further problem of this, initially very readily suitable, material is that, for build-up welding to carry out repairs or to install, for the first time, 15 longitudinal grooves extending in the axial direction for the purposes mentioned in the introduction, controlled welding conditions likewise have to be observed in order to obtain high-quality build-up weld seams.
This problem will be important at the operating site of a roller press with personnel who are untrained especially in respect of the material properties when existing profilings are to be built up by build-up welds over the course of regular maintenance or material preservation. A conventional seam applied by build-up welding which has been produced without giving consideration to the characteristics of this material appears initially to be strong and of a high quality. During operation, however, the base material lying under the build-up seam breaks and the build-up seams detach from the roller casing. Depending on the treatment of the casing, this is therefore no longer repairable.
DE3643259C1 discloses an alloy which has a high chromium content and is suitable for producing rollers which are used for rolling in hot strip rolling mills. The alloy having a high chromium content which is disclosed therein is distinguished by the fact that the roller forms no impressions during use and does not stick to the rolling stock. Nothing is known from DE3643259C1 in relation to further particular suitable uses of this alloy.